Cynically, I suspect that they wanted to cut staffing costs by 50% and this was seen as an easy way to justify it without going through a consultation process.
The reason it would be a cynical view is that firing a lot of people for failing to reach some required standard wouldn't be classed as redundancy, but a firing. This also reflects worse on the affected employees when seeking future employment.
I actually hope some of the people challenge this in court, as there are also regulations around this - if the people had already passed their probation period, and especially if they had already been working a significant length of time without issue, and then fired because of this test, it might well be found to be unfair dismissal. And, as I said before - if over 50% of your workforce don't know your policies, that shows a failure in management for not providing adequate training, not a reflection of the employees.